Rafael Nadal has weighed in on Wimbledon's scheduling debate, hitting back at suggestions Ash Barty deserved to play on Centre Court over him on Manic Monday.

Despite entering the grand slam as the top seed and world No. 1, Barty played just one of her four matches on the biggest stage and she'll have to wait another year to set foot on tennis's most famous turf after she lost last night in three sets to American Alison Riske.

Barty's match against Riske on Court No. 2 provided plenty of entertainment as it went the distance and it's been a constant theme of the year's third grand slam about whether she deserved top billing more than just once.

A few days ago the Queenslander's doubles partner Victoria Azarenka blasted the inequality in scheduling between men and women, saying the male players are given more exposure.

But when Nadal was asked if his match against Joao Sousa — which the Spaniard won easily 6-2 6-2 6-2 in one hour and 45 minutes — should have been played elsewhere to accommodate Barty on Centre Court given it turned into a fizzer, he defended his right to stay in the spotlight.

Nadal said there's no way of knowing whether a match scheduled for Centre Court will turn out to be exciting or not and said it's not fair to attack those tasked with the difficult job of working out who plays where.

He also said he is ahead of Barty in terms of his standing in the sport.

"Can we predict the future or not?" Nadal said, before he smiled and responded lightheardly when a reporter reminded him Barty was world No. 1. "I am the world No. 2 and I won 18 grand slams.

"My answer is not no or yes. My answer is they (organisers) make a decision. You are putting Ashleigh Barty in front of me. For me, both decisions are good.

"In the world of tennis today, honestly, my feeling is today I am little bit more than Ashleigh Barty, even if Ashleigh Barty is the first player of the world and she already won the French Open and she is playing unbelievably good.

"But we can't create polemics every single day about decisions that they (organisers) have to take. At the end of the day they have to make a decision.

"A day like today, everybody is playing, of course (Novak) Djokovic is not playing in the Centre Court. For me the first day I have been playing in the Court 1. I played in (French Open secondary court) Suzanne Lenglen in Roland Garros, if I'm not wrong, in the second round.

"Every day is a decision. We cannot create polemics about that. Court No. 2, OK, they have to make decisions. Today they probably decided that. They have other girls playing on the Centre Court now."

Serena Williams booked her place in the quarter-finals, where she'll face Riske, after a straight sets demolition of Carla Suarez Navarro on Court No. 1 today. The American said she's "not here to complain about a lot of stuff unless I need to" and was more than happy to not be on Centre Court.

But she agreed men's matches in general are promoted with much more vigour than women's matches and backed Azarenka's stance.

"Of course, the women's matches aren't pushed as much as the men's matches to be on the marquee courts," Williams said. "I think there are some players that are pushed more than others.

"With what I believe, just trying to get equality for women to be treated the same way, it's important to have those voices like Vika's voice to be loud."

While some on social media have been complaining about Barty's lack of Centre Court action on her behalf, the woman herself isn't buying into any of the talk.

The 23-year-old has played a straight bat to any questions about scheduling since her Wimbledon campaign started and she didn't deviate from her game plan when quizzed about the matter after her defeat to Riske.

"Scheduling is out of my control. I'll play on any court I'm scheduled on," Barty said.

"I think obviously scheduling is very difficult. There are so many incredible matches all the fans and all the people want to watch, and players want to be a part of.

"For us, the tennis court is the same size. The surroundings change, yes. They're a little bit different. No matter what court you're scheduled on, it shouldn't matter how you approach the match or play. It certainly doesn't for me.

"Court 2 is a beautiful court here. We played on that court earlier in the rounds and for a doubles match, as well. It's a beautiful court. I enjoyed my time out there."

NOTABLE MEN'S RESULTS

Roger Federer bt Matteo Berrettini 6-1 6-2 6-2, Novak Djokovic bt Ugo Humbert 6-3 6-2 6-3, Kei Nishikori bt Mikhail Kukushkin 6-3 3-6 6-3 6-4, David Goffin bt Fernando Verdasco 7-6 2-6 6-3 6-4, Guido Pella bt Miloas Raonic 3-6 4-6 6-3 7-6 8-6.